The present invention relates to an interference control technique between base stations in a wireless communication system.
In these years, wireless communication systems in compliance with the LTE (Long Term Evolution) standard whose maximum communication speed exceeds 100 Mbit/s begin to put to practical use. In LTE, multipath resistance is improved using OFDMA (Orthogonal Frequency Division multiple Access) for downlink access and SC-FDMA (Single Carrier-Frequency Division Multiple Access) for uplink access, and spectrum efficiency is improved by introducing MIMO (Multiple-Input Multiple-Output) transmission in which a transmitter receiver uses a plurality of antennas.
In a cellular system, a communication area covered by a base station is called a cell. A base station whose transmission power is large and that covers a broad communication area is called a macro base station, and the communication area of the macro base station is called a macro cell. In the cellular system, macro base stations are distributed and disposed in a service area, so that a fewer number of base stations cover a broad area in the overall system. However, there are areas to which radio waves from a macro base station are hardly delivered in underground areas, upper stories of buildings, and areas behind buildings, for example. These areas are called blind zones. In addition to this, in these years, because of the spread of smartphones, wireless traffic is rapidly increased, and it becomes difficult to accommodate wireless traffic using only macro base stations.
For the purposes of elimination of these blind zones and off-loading traffic in macro base stations, small-sized base stations such as a pico base station and a femto base station are disposed whose transmission power and communication area are small. The communication areas of these small-sized base stations are called a pico cell and a femto cell, for example. A network topology in which base stations with small transmission power (Low Power Node: LPN) such as a pico base station and a femto base station are disposed in the communication area (the macro cell) of a macro base station is called a Heterogeneous Network (HetNet). Various studies are conducted on a point that interference from a macro base station with a large transmission power greatly degrades the communication quality of users connected to the LPN, which is a technical problem of the HetNet.